The field of the invention is rinsing and drying of semiconductor substrates. More specifically, the invention relates to methods and devices for drying semiconductor substrates using a surface tension effects.
During the processing of semiconductor substrates into electronic devices, such as integrated circuits, it is necessary to rinse and dry the semiconductor substrates. The rinsing process removes residual chemicals, particulate matter, and contaminants from the semiconductor substrates. Chemical residues and contaminants that are not removed during the rinsing and drying steps reduce the overall yield of the manufacturing process. This reduces the number of usable electronic components, such as integrated circuits, microprocessors, memory devices, etc., that can be obtained from a semiconductor substrate. Contamination problems are particularly troublesome in current semiconductor processes where an increasing, number of ever smaller electronic devices are formed on a semiconductor substrate. As semiconductor manufacturing technology advances, the electronic devices formed on the substrates have become progressively smaller, so that more devices are fit onto the substrate, to provide ever more sophisticated, versatile, and economic electronic end products. However, as a result, contamination becomes even more difficult to control, as even smaller particles can act as contaminants. Consequently, ever smaller particles must be removed or excluded. As avoiding contamination caused by smaller particles is more difficult than avoiding contamination by larger particles, rinsing and drying semiconductor substrates now presents additional design challenges.
To reduce contamination, various surface tension effect techniques have been used. Two of the most widely used are thermocapillary and solutocapillary techniques. U.S. Pat. No. 4,722,752 (Steck) teaches that the use of warm or hot water, with the subsequent reduction in surface tension, can aid in the drying of a semiconductor wafer through a combination of evaporation and low surface tension.
U.S. Pat. Nos. 4,911,761 (McConnell et al.), 5,271,774 (Leenaars et al.), 5,807,439 (Akatsu et al.), and 5,571,337 (Mohindra et al.), and European Patent Specification No. 0 385 536 B1. (Lenaars et al.). describe solutocapillary techniques
McConnell et al. uses a relatively thick layer of an organic solvent such as isopropyl alcohol (IPA) on the surface of a liquid such as water, within a closed and preferably heated process vessel. The layer of solvent is then allowed to recede over the semiconductor wafers. The organic solvent creates a displacement of the water on the liquid surface, effectively diluting the water near the surface. This reduces the surface tension of the surface region, causing displacement of water on the wafer surface by the organic solvent.
Mohindra et al. teaches that draining water slowly over the surface of a semiconductor wafer while simultaneously introducing IPA in dilute form causes a lowering of the surface tension of the surface region of the water. The reduced surface tension located adjacent to the face of the semiconductor wafer promotes the removal of water from the work piece. The Mohindra et al. apparatus dries the wafers without substantial movement of the wafers. However, non-uniform drying (from the top of the wafer to the bottom) may result due to an accumulation of contaminants at the surface layer of the water. Since the liquid at the surface is unable to cascade once the water first starts to recede, an increasing concentration of contaminants builds near the surface layer as the water level decreases. The accumulation of contaminants, and particularly organic contaminants, alters the surface tension gradient as a function of time and position along the face of the semiconductor wafer.
Lenaars et al. describes the introduction of an organic solvent, such as IPA, in the presence of a continuously refreshed surface layer of water while simultaneously moving the wafers through the liquid-gas interface. A Marangoni effect flow is produced, creating a region of low surface tension directly adjacent to the semiconductor wafer surface. As is well known in the field, the Marangoni effect produces a flow of liquid from the region of low surface tension to a region of high surface tension.
In McConnell et al. and Mohindra et al., the semiconductor wafers are held in a stationary position during the rinsing and drying steps. In Mohindra et al., the water in the process vessel is drained over the wafers, which produces an inconsistent and constantly changing surface tension from the top of the work piece to the bottom. In McConnell, there is less inconsistency. However, there is still non-uniform surface tension, because the layer of IPA on the surface of the water changes from the top of the vessel to the bottom of the vessel.
In Lenaars et al., this phenomena is reduced by maintaining an overflow of the water at the surface, while introducing an organic vapor continuously during the drying phase. However, movement of the semiconductor wafers during processing is required. Having to move the wafers is disadvantageous because additional components are required, adding to the mechanical complexity, and reducing the reliability of the apparatus. In addition, the movement increases the risk of damage to the wafers during transfer into and out of the liquid.
Accordingly, there is a need for a apparatus and method for rinsing and drying semiconductor substrates that: (1) efficiently removes residual chemicals, particulate matter, organic species, and contaminants from semiconductor substrates; (2) does not produce a gradient of trapped organic species as measured from the top to the bottom of the semiconductor substrate; (3) removes water and contaminants from the surface of the semiconductor substrates; and (4) does not move the semiconductor substrates during rinsing/drying operations.
In a first aspect of the invention, a processor for rinsing and drying semiconductor substrates is disclosed. The processor includes an outer containment vessel that holds an inner process vessel. One or more semiconductor substrates are loaded within the process vessel. The semiconductor substrates are held stationary within the process vessel. The process vessel includes porous walls which permit the transfer of fluid from the process vessel to the outer containment vessel.
In a second separate aspect of the invention, in a method for rinsing and drying a semiconductor substrate, a processing fluid is introduced into a process vessel. The processing fluid bathes a stationary semiconductor substrate in the process vessel. A dilute organic vapor is introduced above the processing fluid in the process vessel. The processing fluid is evacuated from the process vessel to expose the semiconductor substrate. A lateral Marangoni effect flow is produced on the surface region of the processing fluid contained within the process vessel. The flow originates from the semiconductor substrate and travels across the processing fluid surface region and through a porous wall of the process vessel, into an outer containment vessel. The invention resides in subcombinations of the foregoing features as well.
These aspects provide for a constant uniform concentration gradient of organic liquid on the surface of a processing fluid where a meniscus comes into contact with a semiconductor substrate, while keeping the semiconductor substrate stationary during processing.
It is an object of the invention to provide an improved method and apparatus for rinsing and drying a workpiece.